•T and R vary
smoothly (and together) along the main sequence
•B stars are ~4
times hotter and ~10 times bigger than sun
•M stars are ~2
times cooler and ~10 times smaller than sun
•Presence of a
line implies that a single fundamental property
is varying to make some stars B stars
and some stars M stars
•That fundamental
property then controls T, R
•A second property
controls whether we get a giant or dwarfs
•